Caption: Iron nail in salt water and air. Experiment to show the corrosive effects of different combinations of water and air on iron. Here the nail is in a beaker partially filled with salt water, with air in the remaining half. Iron rusts (corrodes) in the presence of oxygen and water with salt accelerating the process. In normal air corrosion tends to happen slowly as the amount of water is quite low. Here the presence of water has made the air very damp and so the top half is rusting. However the nail is rusting more quickly under the water. Rust (iron oxide, brown) deposits can be seen at the bottom of the beaker.